1. Technical Field
The present invention relates to data transfer devices that perform authentication processing with a plurality of devices and that transfer data to the plurality of devices.
2. Background Information
Various devices, such as compact disk (CD) changers, digital versatile disk (DVD) players, digital broadcasting receivers, monitors, and amplifiers, are installed in vehicles, so that users can enjoy music and pictures by selecting corresponding devices. Connecting these devices using digital buses, such as IEEE 1394 buses, enables high-quality data transfer, and music with high-quality sound and pictures with high image quality can thus be produced.
Some content recorded on DVDs or some content distributed using digital broadcasting may include copy control information for copy restriction in terms of copyright protection. For example, in order to play back a DVD for DVD-Video and to transfer picture data to a monitor, a DVD player transfers picture data encrypted using copy control information recorded on the DVD, and a monitor that receives the encrypted picture data decrypts the details of the picture data and displays the decrypted picture data.
Various algorithms exist as technologies for protecting content to be transferred. For example, a procedure in which key exchange necessary for encrypting and decrypting content is performed after authentication between devices is performed is described in Japanese Unexamined Patent Application Publication No. 2003-30054 (second to ninth pages, FIGS. 1 to 8).
As described in Japanese Unexamined Patent Application Publication No. 2003-30054, in a case where key exchange is performed after authentication between devices is performed, when a sending device transfers content to a plurality of receiving devices, the plurality of receiving devices acquire keys to decrypt the content at different time periods from each other. This causes a user who tries to look at and listen to the details of the content to feel dissatisfied.
FIG. 8 illustrates a specific connection example of a plurality of devices. Referring to FIG. 8, a DVD player 200 is connected to monitors 210 and 212 and an amplifier 214 via IEEE 1394 buses 220. In order to decrypt and display the details of picture data of content sent from the DVD player 200 using the monitors 210 and 212 and in order to decrypt, using the amplifier 214, and generate, using a speaker, the details of music data of the content, authentication and key exchange must be performed between the DVD player 200 and the monitor 210, between the DVD player 200 and the monitor 212, and between the DVD player 200 and the amplifier 214 before the monitors 210 and 212 and the amplifier 214 perform processing. For example, first, if key exchange is performed after authentication processing between the DVD player 200 and the monitor 210 is completed, a certain amount of time (for example, about one second) is required for displaying the details of content after the key exchange. Then, if key exchange is performed after authentication processing between the DVD player 200 and the monitor 212 is completed, a certain amount of time (for example, about one second) is required for displaying the details of the content after the key exchange. Finally, if key exchange is performed after authentication processing between the DVD player 200 and the amplifier 214 is completed, a certain amount of time (for example, about one second) is required for generating music as the details of the content after the key exchange. Accordingly, after the monitor 210 displays the details of the content, about two seconds are required for generating music corresponding to the details. During this time, only a picture is displayed without sound. Thus, a user feels dissatisfied since the user implicitly expects that pictures and music are generated output at the same time. The time required for generating music corresponding to the details of content after a picture is displayed increases in accordance with an increase in the number of connected devices for which authentication is required.